I wouldn't think that even in the Civil War that a soldier could walk into town carrying his rifle with him anytime he wanted to. The photograph is certainly staged. I don't see this photograph being taken in Camp. It would appear that it was taken in a studio. The lighting is too good and the picture is too clear for it to have been taken from a mobile studio. I can see Brownell being able to walk by the camp pickets and Guards with his accouterment, but not his rifle. Hense the two bayonets.
I do get tickled at those who say that a certain regiment was armed with a certain weapon such as the Pistols and big Bowie knives because of a photograph like this where Brownell is carrying the dagger that was mentioned. The Bayonet that he wore is more indicative of what weapon he actually carried than the weapon he held in his hand in the picture. But as you know that bayonet, although rarer than the typical socket bayonet, still fit a number of different weapons.